Strange metal behavior of the Hall angle in twisted bilayer graphene

Twisted bilayer graphene (tBLG) with interlayer twist angles near the magic angle ~1.08º hosts flat bands and exhibits correlated states including Mott-like insulators, superconductivity and magnetism. We will discuss our recent measurements on a tBLG device with a twist angle of 0.93º, below the magic angle. We find in addition to Mott-like insulator and superconducting states near half filling, evidence for a novel correlated state at five electrons/moire´ unit cell. Our results reveal that the magic range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG. Out latest measurements of the superconducting phase in tBLG will be discussed. Moreover, we will discuss combined temperature-dependent transport measurements of the longitudinal and Hall resistivities in close to magic-angle tBLG. While the observed longitudinal resistivity follows linear temperature T dependence consistent with previous reports, the Hall resistance shows an anomalous T dependence with the cotangent of the Hall angle ~ T². Boltzmann theory for quasiparticle transport predicts that both the resistivity and the Hall angle cotangent should have the same T dependence, contradicting the observed behavior. This failure of quasiparticle-based theories is reminiscent of other correlated strange metals such as cuprates.